A general vehicle travels by using energy which is generated by burning an air-fuel mixture in an engine. Recently, in order to respond to strengthened exhaust gas regulations and improve fuel efficiency, a hybrid vehicle is increasingly used.
The hybrid vehicle means a vehicle using two or more power sources. In general, the hybrid vehicle includes an internal combustion engine which is driven by burning fossil fuel, and a motor which is driven with electric energy stored in a battery as power sources.
As a battery of 48 V is applied to the vehicle, an interest in a mild hybrid vehicle is increased. The mild hybrid vehicle uses an engine as a main power source, and uses a motor as an assistance of the engine. That is, the motor of the mild hybrid vehicle is generally connected to the engine to start the engine, assists with torque during a driving of the engine, and charges a battery by using excess energy during the driving of the engine.
In the meantime, the exhaust gas generated during a combustion process includes various materials (for example, hydrocarbon, carbon dioxide, and nitrogen oxide), and in order to respond to an environment regulation, some of the various materials contained in the exhaust gas need to be removed.
In general, the exhaust gas discharged from the engine through an exhaust manifold is introduced to a catalytic converter that is installed in an exhaust pipe and is purified, is then passed through a muffler to decrease noise, and then is discharged to the air through a tailpipe. The catalytic converter purifies contaminant materials included in the exhaust gas. Further, a soot filter for collecting particulate matters (PM) included in the exhaust gas is mounted on the exhaust pipe.
The soot filter includes a wall made of a porous material, and when the exhaust gas passes through the wall, the PM included in the exhaust gas cannot pass through the wall and is collected in the soot filter. According to an increase in the quantity of PM (that is, soot) collected in the soot filter, an area of the wall, through which the exhaust gas may pass, is decreased. Accordingly, back pressure is increased and a performance of the engine is deteriorated. Accordingly, the soot collected in the soot filter needs to be removed at an appropriate time, and this process is referred to as regeneration of the soot filter.
The regeneration of the soot filter is performed by increasing a temperature of the exhaust gas and burning the soot collected in the soot filter, and in order to burn the soot, a temperature of the exhaust gas needs to be at least 650° C.
According to a method of regenerating a soot filter in the related art, when the quantity of soot collected in the soot filter is equal to or larger than a predetermined quantity, a temperature of exhaust gas is increased by post-injecting fuel. That is, a temperature of the exhaust gas is not directly increased through combustion, but a temperature of the exhaust gas is indirectly increased by making post-injected fuel flow into an exhaust pipe to facilitate an oxidation-reduction reaction between the exhaust gas and unburned fuel. Further, the unburned fuel also facilitates oxidation of soot in a soot filter. When a temperature of the exhaust gas is indirectly increased, heating of the soot filter requires a lot of time. Further, the regeneration of the soot filter is frequently stopped by a change in an operation condition during the heating of the soot filter. Accordingly, there is a need for a technology for decreasing a heating time of the soot filter.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.